Monolithic integration of VCSELs with graphene/PEDOT:PSS photodetectors for compact optoelectronics.

Monolithic integration of vertical-cavity surface-emitting lasers (VCSELs) with photodetectors is critical for developing compact optoelectronic systems. However, this integration remains challenging due to the fundamental thermal incompatibility between high-temperature III-V epitaxy and the thermally sensitive active region of VCSEL. Herein, we demonstrate a monolithically integrated device by directly coupling a VCSEL with a graphene/PEDOT:PSS van der Waals heterostructure-based photodetector via a low-temperature approach (<120°C), thus circumventing thermal damage associated with conventional high-temperature epitaxy. The integrated VCSEL exhibits excellent spectral stability with a minimal emission wavelength shift (<3 nm), while the optimized detector features enhanced near-infrared (NIR) absorption and a peak responsivity of up to 2.1 A/W at 940 nm. Functioning as a compact optical transceiver, the device enables lens-free reflection detection over distances up to 3 cm and short-range optical transmission with lens assistance. Benefiting from graphene's zero-bandgap property, the detector is inherently compatible with 850 nm VCSEL without the need for customized epitaxy, significantly simplifying fabrication complexity and reducing costs. This scalable low-temperature scheme provides an effective strategy to overcome thermal incompatibility in conventional III-V monolithic integration, offering a promising low-cost solution for advanced compact optoelectronic systems.